ipq40xx: fix AVM NAND caldata extraction

ipq40xx: fix AVM NAND caldata extraction

The AVM Fritz!Box 7530 (and probably other AVM IPQ4019 NAND devices)
has it's caldata not stored consistently, but instead at currently
3 known possible offsets.

As we get a non-zero exit code from fritz_cal_extract, simply try all
three possible offsets on both bootloader partitions, until a matching
caldata for each radio is found.

Reported-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: David Bauer <mail@david-bauer.net>
(cherry picked from commit a6f85b81b7efd3fa3265d70e5406275b2dc03f5f)